Long term studies on the population biology of two specie of eyefluke, Diplostomum gasterostei and Tylodelphys clavata (Digenea: Diplostomatidae), concurrently infecting the eyes of perch, Perca fluviatilis

Changes in the size of the infrapopulations of metacercariae of Diplostomum gasterostei and Tylodelphys clavata were studied in a small lake for a period of seven years in perch Perca fluviatilis . Tylodelphys clavata appeared in the lake at the commencement of the study and its subsequent population increase and changes were typical of those of a species recently established in a new habitat. Population size increased slowly at first, then rapidly, then declined again as population density approached equilibrium level. By contrast, the population size of D. gasterostei declined throughout the study. Two processes were responsible for the decline: a decrease in the proportion of fish carrying heavy infections which was continuous throughout the seven years and a dramatic decline in recruitment rate in young fish during the last two years. In earlier years recruitment rate had changed annually and changes in overall infrapopulation size had largely reflected the recruitment rate two years previously. It was concluded that these two processes were independent of each other and related to changes in the population density of other species of eyeflukes. The decline in the proportion of heavily infected fish was significantly negatively correlated with the increase in population density of T. clavata and the decline in recruitment rate in young fish was coincident with the appearance and infrapopulation increase of T. podicipina metacercariae in the eyes of young perch. It is suggested that these two species interact negatively with D. gasterostei and are currently partitioning the perch habitat between themselves.     

The population biology of two species of eyefluke, Diplostomum gasterostei and Tylodelphys clavata, in perch

Incidence, intensity and frequency distributions of infections in perch, Perca fluviatilis , with the eyeflukes Tylodelphys clavata and Diplostomum gasterostei were studied in a lake at monthly intervals over a period of two years. T. clavata had appeared in the lake immediately prior to the study, and its levels of infection continued to rise throughout the period of investigation whereas those of D. gasterostei remained relatively steady. The main period of infection of fish by both species of parasites was late summer, but a second and minor infection took place in spring. In the first year after its introduction T. clavata exhibited a seasonal cycle in incidence and intensity of infection and disappeared from fish in summer, but in the second year this cycle was masked by increased variation in development times and lack of synchrony throughout the parasite population. It is concluded that T. clavata has a life span of one year or less and that the parasites die within the fish, mainly in summer. D. gasterostei in contrast has a life span of at least one year, and disappearance of the parasite from the population is probably due to death of some heavily infected fish, although it was not possible to determine if this was due directly to the presence of the parasite.     

The population dynamics of eyeflukes Diplostomum spathaceum and Tylodelphys clavata (Digenea: Diplostomatidae) in rainbow and brown trout in Rutland Water: 1974–1978

The development of populations of eyeflukes Diplostomum spathaceum and Tylodelphys clavata in trout introduced into Rutland Water is related to the availability of infected Limnaea pereger, the first intermediate host, and the differential resistance to eyeflukes in Salmo gairdneri and S. trutta. The numbers of snail and fish intermediate hosts were monitored from impoundment of the Gwash in 1974 to completion of the reservoir in 1978. High infection rates in coarse fish in the feeder streams in 1974 are related to high infection rates in Limnaea pereger. Large eyefluke populations in introduced rainbow trout but not in brown trout confirm their differential resistance. Differences in levels of infection in seine-netted and rod-caught rainbow trout suggest that heavily infected fish could not respond to the fishermens' lures. Reduced numbers of eyeflukes in rainbow trout from 1979 onwards are related to the vast increase in volume of the reservoir in 1977 and decrease in abundance of Limnaea pereger.     

The population biology of two species of eyefluke, Diplostomum spathaceum and Tylodelphys clavata, in roach and rudd

Infections of roach ( Rutilis rutilus ), and rudd ( Scardinius erythrophthalmus ), by the eyeflukes Diplostomun spathaceum and Tylodelphys clavata were studied in a lake over a three year period. T. clavata first appeared at the beginning of the study. Roach were heavily infected by both parasites, whereas the rudd contained very few specimens of either species. A small number of roach-rudd hybrids were also examined, and appeared to have a susceptibility intermediate between the parental types.
Levels of T. clavata in roach increased throughout the study. This parasite had a life span of a year or less in the fish, and was continuously lost from the population. This loss was balanced by a minor infection period in April/May and a major one extending from August until January. The fish continued to accumulate infections until they reached a size of about 130 mm, but thereafter intensity fluctuated about the level reached.
D. spathaceum infections similarly increased throughout the period of study, and there was a suggestion of a wave of infection in the spring. This parasite has a much longer life span, and levels of infection increased with fish size, only falling in the largest, and therefore oldest, hosts.
The major changes in the parasite populations in the roach were reflected, to a lesser extent, in the rudd. Both species were over-dispersed, but the data from roach was too heterogeneous to fit to any theoretical models, whereas that from the rudd was found to conform to a Negative Binomial distribution.     

Chromosomal apparatus of trematodes of the general Diplostomum and Tylodelphys (Strigeidida, Diplostomatidae) and its taxonomic significance

The chromosomal apparatus of three species of trematodes of Diplostomum (D. spathaceum, D. indistinctum, D. mergi) and one species Tylodelphys (T. clavata) is described. It has been suggested that karyological investigations can be used for taxonomic purposes. The opinion has been expressed that the number of chromosomes in the karyotype of these trematodes plays no taxonomic role. Of great taxonomic significance are the size and morphology of chromosomes. Differences in karyotypes of trematodes belonging to different species and genera were revealed by these characters. The absence of close dependence between morphology of adult and specific peculiarities of karyotypes in species of the same genus enables in some cases the use of chromosomal apparatus as a most reliable criterion for a differentiation of close species.     

New metacercariae of the genus Tylodelphys (Trematoda, Diplostomatidae) in lacustrine populations of Galaxias maculatus (Teleostei, Galaxiidae)]

Metacercariae of three new species of Tylodelphys (Trematoda, Diplostomatidae) were found in the brain of Galaxias maculatus (Teleostei, Galaxiidae), at the Meliquina Lake, Neuquen Province, Argentina. These metacercariae are morphologically described as Tylodelphys argentinus n. sp., Tylodelphys barilochensis n. sp. and Tylodelphys crubensis n. sp. This is the first time that a stage of genus Tylodelphys is mentioned parasitizing Galaxias maculatus. Metacercariae of T. barilochen sis n. sp. were also found in G. maculatus brain at the Perito Moreno Lake, Rio Negro Province, Argentina.     

Population dynamics of Tylodelphys destructor and Diplostomum mordax (Digenea: Diplostomidae) co-occurring in the brain of Patagonian silversides from Lake Pellegrini,Patagonia, Argentina

Studies on infection patterns of diplostomid parasites in commercially exploited fishes have not been done in Patagonia (Argentina). The aim of this work was to study the population dynamics of two diplostomid species in the brain of patagonian silversides (Odontesthes hatchery), the interaction between them, and effect on health and physical condition of the hosts. Tylodelphys destructor and Diplostomum mordax metacercariae in the brain of Patagonian silversides in Lake Pellegrini were studied between January 1991 and February 1992. Tylodelphys destructor parasitized all silversides examined; prevalence of D. mordax varied between 7% and 100%. Mean intensity for T. destructor was 35-140 and for D. mordax was 3-49. Highest mean intensities of T. destructor coincided with the lowest mean intensities of D. mordax. Recruitment seems to occur from July-November for T. destructor and from April-June for D. mordax, revealing a temporal segregation with inverse patterns of infection and recruitment. Tylodelphys destructor has higher intensities in the brain of the older fish, whereas D. mordax did not, suggesting another type of segregation. There were no evidences of gross pathology. No covariation between abundance of larvae and condition factor, gonadosomatic index, and gut fullness was detected.     

Infection patterns of Tylodelphys barilochensis and T. crubensis (Trematoda: Diplostomatidae) metacercariae in Galaxias maculatus (Osmeriformes: Galaxiidae) from two Patagonian lakes and observations on their geographical distribution in the southern Andean region,Argentina

In the Patagonian Andean region, 2 species of diplostomatids parasitize the brains of Galaxias maculatus.The purpose of this study was to evaluate seasonal variation, spatial variation, and association with host age in the transmission of Tylodelphys barilochensis and T. crubensis in several oligotrophic lakes in Argentinian Patagonia. Fishes were captured monthly in Lake Gutiérrez and bimonthly in Lake Escondido. One summer or autumn sample was also taken in several other Patagonian lakes. Infection parameters were calculated and compared using nonparametric tests. The 2 species co-occurred in most of the sampled lakes, with high values of prevalence and mean intensity. In Lake Gutiérrez and Lake Escondido, the intensity of both diplostomatid species did not show significant differences between sexes and co-varied with host length. All age classes were infected; maximum prevalence values were reached before maximum mean intensity values in the 1-yr age class. A seasonal pattern of prevalence and mean intensity of the 2 parasite species with autumn mean intensity values differing significantly from those of the other seasons was evident only in Lake Gutiérrez.     

Molecular phylogeny of Diplostomum,Tylodelphys, Austrodiplostomum and Paralaria (Digenea: Diplostomidae) necessitates systematic changes and reveals a history of evolutionary host switching events

The Diplostomidae Poirier, 1886 is a large, globally distributed family of digeneans parasitic in intestines of their definitive hosts. Diplostomum and Tylodelphys spp. are broadly distributed, commonly reported, and the most often sequenced diplostomid genera. The majority of published DNA sequences from these genera originated from larval stages only, which typically cannot be identified to the species level based on morphology alone. We generated partial large ribosomal subunit (28S) rRNA and cytochrome c oxidase subunit 1 (cox1) mtDNA gene sequences from 14 species/species-level lineages of Diplostomum, six species/species-level lineages of Tylodelphys, two species/species-level lineages of Austrodiplostomum, one species previously assigned to Paralaria, two species/species-level lineages of Dolichorchis and one unknown diplostomid. Our DNA sequences of 11 species/species-level lineages of Diplostomum (all identified to species), four species/species-level lineages of Tylodelphys (all identified to species), Austrodiplostomum compactum, Paralaria alarioides and Dolichorchis lacombeensis originated from adult specimens. 28S sequences were used for phylogenetic inference to demonstrate the position of Paralaria alarioides and Dolichorchis spp. within the Diplostomoidea and study the interrelationships of Diplostomum, Tylodelphys and Austrodiplostomum. Our results demonstrate that two diplostomids from the North American river otter (P. alarioides and a likely undescribed taxon) belong within Diplostomum. Further, our results demonstrate the non-monophyly of Tylodelphys due to the position of Austrodiplostomum spp., based on our phylogenetic analyses and morphology. Furthermore, the results of phylogenetic analysis of 28S confirmed the status of Dolichorchis as a separate genus. The phylogenies suggest multiple definitive host-switching events (birds to otters and among major avian groups) and a New World origin of Diplostomum and Tylodelphys spp. Our DNA sequences from adult digeneans revealed identities of 10 previously published lineages of Diplostomum and Tylodelphys, which were previously identified to genus only. The novel DNA data from this work provide opportunities for future comparisons of larval diplostomines collected in ecological studies.     

Long-term stability and effective population size in North Sea and Baltic Sea cod (Gadus morhua)

DNA from archived otoliths was used to explore the temporal stability of the genetic composition of two cod populations, the Moray Firth (North Sea) sampled in 1965 and 2002, and the Bornholm Basin (Baltic Sea) sampled in 1928 and 1997. We found no significant changes in the allele frequencies for the Moray Firth population, while subtle but significant genetic changes over time were detected for the Bornholm Basin population. Estimates of the effective population size ( N _e ) generally exceeded 500 for both populations when employing a number of varieties of the temporal genetic method. However, confidence intervals were very wide and N _e 's most likely range in the thousands. There was no apparent loss of genetic variability and no evidence of a genetic bottleneck for either of the populations. Calculations of the expected levels of genetic variability under different scenarios of N _e showed that the number of alleles commonly reported at microsatellite loci in Atlantic cod is best explained by N _e 's exceeding thousand. Recent fishery-induced bottlenecks can, however, not be ruled out as an explanation for the apparent discrepancy between high levels of variability and recently reported estimates of N _e  << 1000. From life history traits and estimates of survival rates in the wild, we evaluate the compatibility of the species' biology and extremely low N _e / N ratios. Our data suggest that very small N _e 's are not likely to be of general concern for cod populations and, accordingly, most populations do not face any severe threat of losing evolutionary potential due to genetic drift.     

In vitro excystment of the black spot trematode Uvulifer ambloplitis (Trematoda:Diplostomatidae)

Spellman S. J. and Johnson A. D. 1987. In vitro excystment of the black spot trematode Uvulifer ambloplitis (Trematoda:Diplostomatidae). International Journal for Parasitology17: 897–902. Metacercariae of U. ambloplitis became activated and excysted in both acid pepsin and acidified Locke's balanced salt solution (BSS). The maximum percentage of excystment was 40% in acid pepsin and 4% in Locke's BSS. Acid pretreatment was required for the additional excystment that occurred in the pretreatment reductant sodium dithionite, or in an incubation medium, or in a sodium dithionite-incubation medium sequence. Since larvae excysted during both pretreatments and in incubation media, maximum overall excystment percentages were obtained with three treatments; (1) 0.5% pepsin at pH 2.0 for 30 min, (2) 0.2% sodium dithionite at pH 7.4 for 10 min and (3) an incubation medium of 0.2 or 0.5% ox bile salts a pH 7.4 for 120 min, 66 and 79%, respectively. Excystment occurred in trypsin alone or trypsin containing incubation media following pepsin pretreatment or a pepsin-sodium dithionite sequence, but the larvae were sluggish and died within a few min after excysting. Thus, a synergistic effect between bile salts and trypsin was not found in this study. Excystment was primarily an active process with the larva emerging from the narrow end of the parasite cyst, although a breakdown of the host cyst and some softening of the parasite cyst was observed.     

Genetic and morphologic differentiation of Bolbophorus confusus and B. levantinus (Digenea: Diplostomatidae), based on rDNA SSU polymorphism and SEM

Metacercariae of Bolbophorus species are serious pathogens of farmed fish. Molecular diagnostic tools, capable of identifying and differentiating these parasites, may assist in the development of rationale control strategies. The rDNA 18S (small sub-unit: SSU) genes of adult B. confusus and B. levantinus obtained from a pelican, Pelecanus onocrotalus, and a night heron, Nycticorax nycticorax, respectively, were amplified, sequenced, and aligned. Based on this alignment, we developed a genetic differentiation assay between B. confusus and B. levantinus. These 2 species were compared genetically with the North American species B. damnificus and Bolbophorus sp. ('Type 2'). The relationship between species is outlined and discussed. In addition to the molecular study, specimens of B. confusus and B. levantinus were compared morphologically, using scanning electron microscopy. Morphologic analysis revealed interspecific differences in details of the holdfast organ and the position of the acetabulum.     

Diplostomum commutatum (Diesing, 1850) Dubois, 1937 (Trematoda: Diplostomatidae) cercaria

The cercaria of D. commutatum from the mollusk Radix ovata is described. Data on the biology and development of the cercaria up to the metacercarial stage are given. Cercariae of D. commutatum differ from all known species of the genus Diplostomum by a characteristic cuticular armament.     

Phylogeny and classification of the Digenea (Platyhelminthes: Trematoda)

Complete small subunit ribosomal RNA gene (ssrDNA) and partial (D1-D3) large subunit ribosomal RNA gene (lsrDNA) sequences were used to estimate the phylogeny of the Digenea via maximum parsimony and Bayesian inference. Here we contribute 80 new ssrDNA and 124 new lsrDNA sequences. Fully complementary data sets of the two genes were assembled from newly generated and previously published sequences and comprised 163 digenean taxa representing 77 nominal families and seven aspidogastrean outgroup taxa representing three families. Analyses were conducted on the genes independently as well as combined and separate analyses including only the higher plagiorchiidan taxa were performed using a reduced-taxon alignment including additional characters that could not be otherwise unambiguously aligned. The combined data analyses yielded the most strongly supported results and differences between the two methods of analysis were primarily in their degree of resolution. The Bayesian analysis including all taxa and characters, and incorporating a model of nucleotide substitution (general-time-reversible with among-site rate heterogeneity), was considered the best estimate of the phylogeny and was used to evaluate their classification and evolution. In broad terms, the Digenea forms a dichotomy that is split between a lineage leading to the Brachylaimoidea, Diplostomoidea and Schistosomatoidea (collectively the Diplostomida nomen novum (nom. nov.)) and the remainder of the Digenea (the Plagiorchiida), in which the Bivesiculata nom. nov. and Transversotremata nom. nov. form the two most basal lineages, followed by the Hemiurata. The remainder of the Plagiorchiida forms a large number of independent lineages leading to the crown clade Xiphidiata nom. nov. that comprises the Allocreadioidea, Gorgoderoidea, Microphalloidea and Plagiorchioidea, which are united by the presence of a penetrating stylet in their cercariae. Although a majority of families and to a lesser degree, superfamilies are supported as currently defined, the traditional divisions of the Echinostomida, Plagiorchiida and Strigeida were found to comprise non-natural assemblages. Therefore, the membership of established higher taxa are emended, new taxa erected and a revised, phylogenetically based classification proposed and discussed in light of ontogeny, morphology and taxonomic history.     

Opistholobetines (Digenea: Opecoelidae) in Australian tetraodontiform fishes

Opistholebetine opecoelids are reported following examination of 1,041 individual tetraodontiform fishes, comprising 60 species and seven families, collected in Australian waters between 1986 and 2018. Nine species consistent with Opistholebes Nicoll, 1915, Heterolebes Ozaki, 1935 or Maculifer Nicoll, 1915 were recovered. However, phylogenetic analysis of sequence data, generated for some of these species, suggested that five genera, not three, are required to adequately accommodate these taxa. Thus, the concept and composition for each is revised, Pseudoheterolebes Yamaguti, 1959 nec Gupta, 1968 is resurrected and Parallelolebes n. g. is proposed. Of the nine species examined, five are new. Four new species are from fishes endemic to subtropical and temperate Australian waters for which no trematodes have previously been reported: Pa. australis n. sp. and Ps. corazonae n. sp. from the slender-spined porcupinefish Diodon nicthemerus Cuvier (Diodontidae) off Stanley, Tasmania; Pa. virilis n. sp. from the horse-shoe leatherjacket Meuschenia hippocrepis (Quoy & Gaimard) (Monacanthidae) off Stanley; and Ps. stellaglobulus n. sp. from the threebar pocupinefish Dicotylichthys punctulatus Kaup (Diodontidae) in Moreton Bay, south-east Queensland. The fifth new species is M. diodontis n. sp., collected from the spotted porcupinefish Diodon hystrix Linnaeus and the blackblotched porcupinefish D. liturosus Shaw, in tropical waters on the Great Barrier Reef. Species reported previously include the type-species of Opistholebes, O. amplicoelus Nicoll, 1915 from the rough golden puffer Lagocephalus lunaris (Bloch & Schneider) (Tetraodontidae) and the common toadfish Tetractenos hamiltoni (Richardson) (Tetraodontidae) in Moreton Bay, and three species reported for the first time from fishes in Australian waters: H. maculosus Ozaki, 1935, Pa. elongatus Ozaki, 1937 n. comb. and Ps. diodontis (Cable, 1956) n. comb., each from both D. hystrix and D. liturosus on the Great Barrier Reef. Following the revisions, Opistholebes is recognised for two species, Heterolebes for five, Maculifer for eight, Pseudoheterolebes for five and Parallelolebes for three.     

The Pacific Notocotylus atlanticus (Digenea: Notocotylidae)

Recently two unidentified Notocotylus species have been recovered from a mallard in Hokkaido, Japan. Preliminary data indicated that one of them may belong to N. atlanticus—a species found in Europe and on the Atlantic coast of North America. Now we have sequenced partial cox1 for several European N. atlanticus isolates and performed a barcode gap analysis. It has shown the conspecificity of European and Japanese worms, bringing up discussion on distribution, transmission and host specificity in this species.     

Transmammary infection of free-ranging Florida panther neonates by Alaria marcianae (Trematoda: Diplostomatidae)

Two freshly-dead female Florida panther (FP) neonates, Puma concolor couguar (=Puma concolor coryi), an 11-day-old and a 17-day-old, were collected in the Florida Panther National Wildlife Refuge (26 degrees 14'N, 81 degrees 36'W), Collier County, Florida. The 2 neonates were siblings and had presumably fed only on milk from the dam since birth. A 12-day-old female FP neonate was collected in the Big Cypress National Preserve (26 degrees 05'N, 81 degrees 15'W), Collier County, Florida and had also fed only on milk from the dam since birth. Milk was the only food item found in the gastrointestinal tract of these neonates. Mesocercariae and diplostomula of Alaria marcianae were collected from the lungs of the 3 neonates, indicating a transmammary route of infection. No mesocercariae, diplostomula, or mature A. marcianae were seen in the stomach or small intestine. The probable paratenic host for the A. marcianae infection in the adult Florida panther is the raccoon (Procyon lotor).